Electrolytic refining of copper

ABSTRACT

Copper is electrolytically refined by the series process by immersing unrefined electrodes in series in an electrolyte solution contained in a tank whose inner surface is of an electrically insulating polymeric material that is substantially inert to the electrolyte solution, maintaining the electrolyte solution at a temperature of at least 54*C (129*F), preferably 63*C (145*F), and passing a direct current through the electrolyte to cause copper from one of the electrodes to be dissolved in the solution and deposited as pure copper on another of the electrodes, baffles of an electrically insulating material that is substantially inert to the electrolyte solution being positioned in the tank that flow of current between facing major surfaces of adjacent electrodes is not impeded and flow of current that would otherwise occur around at least some of the immersed edges of electrodes is substantially reduced.

United States Patent [191 Nightingale et al.

[ Dec. 23, 1975 ELECTROLYTIC REFINING OF COPPER [73] Assignee: BritishCopper Refiners Limited,

Prescot, England [22] Filed: Sept. 12, 1973 [21] Appl. No.: 396,550

[52] US. Cl 204/106; 204/108 [51] Int. Cl. C25C 1/12 [58] Field ofSearch... 204/288, 289, 297, 106-108,

204/DIG. 7

[56] References Cited UNITED STATES PATENTS 1,700,178 l/l929 Porzel204/DIG. 7 2,859,166 ll/l958 Grigger 204/297 R FOREIGN PATENTS ORAPPLICATIONS 1,067,297 5/1967 United Kingdom OTHER PUBLICATIONSElectroplating Engineering Handbook, 2nd Ed., by A. K. Graham, 1962, p.485.

ul-IHI-II-Il-Il-I Metal Finishing Guidebook Directory, 1968, pp. 718,720-721.

Primary Examiner-R. L. Andrews Attorney, Agent, or Firm-Webb, Burden,Robinson & Webb [57] ABSTRACT Copper is electrolytically refined by theseries process by immersing unrefined electrodes in series in anelectrolyte solution contained in a tank whose inner surface is of anelectrically insulating polymeric material that is substantially inertto the electrolyte solution, maintaining the electrolyte solution at atemperature of at least 54C (129F), preferably 63C (145F), and passing adirect current through the electrolyte to cause copper from one of theelectrodes to be dissolved in the solution and deposited as pure copperon another of the electrodes, baffles of an electrically insulatingmaterial that is substantially inert to the electrolyte solution beingpositioned in the tank that flow of current between facing majorsurfaces of adjacent electrodes is not impeded and flow of current thatwould otherwise occur around at least some of the immersed edges ofelectrodes is substantially reduced.

5 Claims, 4 Drawing Figures Sheet 1 of 2 3,928,151

US. Patent Dec. 23, 1975 FIG] ELECTROLYTIC REFINING OF COPPER Thisinvention relates to the method of refining copper in which plates ofthe metal to be refined form electrodes, hereinafter referred to asunrefined electrodes, in an electrolytic cell, usually containing anaqueous solution of copper sulphate acidified with sulphuric acid.

In the Specification of our British Pat. No. 1,067,297 there isdescribed and claimed a method of electrolytically refining copper whichcomprises forming a copper strip of indefinite length by a continuouscasting process, cutting this strip into lengths such that plates havingthe required superficial area are formed, preferably of at least 0.74sq.m. (8 sq. ft.), immersing the cut lengths as unrefined electrodes inan electrolyte solution and passing a direct current through theelectrolyte to cause copper to be dissolved from the unrefinedelectrodes and deposited as pure copper.

Owing to their method of manufacture, the unrefined electrode plateshave flatter and smoother surfaces and are more accurate in all theirdimensions than electrodes cast in conventional open moulds and can,therefore, be satisfactorily used in sizes larger than it iseconomically possible to use with electrodes cast individually in openmoulds and/or they can be packed closer together than such electrodes,thus reducing the superficial area of the tank and/or the consumption ofpower for a given output of refined copper.

The advantages provided by unrefined electrode plates formed by acontinuous casting process render these electrodes especially suitablefor use in the series process of electrolytically refining copper, thatis the process in which a plurality of unrefined electrodes aresupported in the electrolyte solution, all of a group of said electrodesexcept the first and last are bipolar, and a direct current enters thegroup at the first electrode or anode at the positive end of the group,generally travels from each intermediate electrode through theelectrolyte solution to the next in line and so forth until it leavesthe group at the last electrode or cathode at the negative end of thegroup. In this way impure copper is dissolved from one side of eachintermediate electrode and pure copper is deposited on the other side ofthe electrode. Because copper is not dissolved from one side of the lastelectrode or cathode, this plate, generally called the starting cathode,is customarily of pure metal and is initially thinner than theintermediate electrodes.

Although unidirectional direct current is normally used in the seriesprocess, the term series process as used herein is not intended toexclude series processes in which the current is reversed for shortperiods.

Owing to the large number of electrodes generally immersed in theelectrolyte in the series process the voltage applied between the anodeand cathode electrodes of the series is relatively high, usually in theorder of 8OV, and in order to prevent current-leakage through the wallsof the tank containing the electrolyte it has been the practice inoperating the series process to make the tank of, or to line the tankwith, an electrically insulating material. Hitherto tanks for use in theseries process have been moulded from a mixture of asbestos, asphalt andsand or have been lined with a mixture of asphalt, mastic and blown oil,but these insulating materials have the serious disadvantage that due totheir relatively low softening temperatures, the

temperature at which the electrolyte can be maintained is limited,usually to a temperature below 45C (113F). By so limiting thetemperature at which the electrolyte is maintained, the consumption ofpower for a given output of refined copper can sometimes be so high thatthe use of the series process can be rendered uneconomical in spite ofits other inherent advantages.

Furthermore, in the electrolytic refining of copper by the seriesprocess it is advantageous to arrange for the gaps between the immersededges of the electrodes and the neighbouring walls of the tank to be assmall as possible because a gap of unnecessary dimension adverselyaffects the electrical efficiency of the process, there being lesstendency for direct current to flow around the immersed edges ofelectrodes when the gap is small. However, with regard to the gapsbetween the immersed bottom edges of the electrodes and the base of thetank, with a view to preventing slime which is released from the impurecopper and which settles on the base of the tank from shorting adjacentelectrodes as it accumulates and to ensure that flow of electrolytesolution is not impeded, it is the general practice to support theelectrodes in the tank in such a way that their bottom edges are spaceda substantial distance from the base of the tank, this distance normallybeing in the region of 300 mm. A gap of such size adversely affects theelectrical efficiency of the series process because there is a tendencyfor direct current to flow around the bottom edges of the electrodes.Furthermore, with regard to the gaps between the immersed side edges ofthe electrodes and the side walls of the tank, it is the generalpractice to space side edges of the electrodes a substantial distancefrom the neighbouring side wall of the tank, usually in the region ofmm, because if the width of the electrodes having regard to the width ofthe tank is arranged to be such that the gaps between the side edges ofthe electrodes and the neighbouring side walls of the tank are small,then since when a large number of electrodes, either in a single groupor in two or more smaller groups, are lowered into or raised from thetank by means of a crane or other overhead support, it is difficult toensure that the side edges of the suspended electrodes are maintained insubstantial alignment, as electrodes are lowered into or raised from thetank there is a danger that side edges of some of the electrodes willscore or otherwise damage the inner surfaces of the tank. Since in thecase of the series process the inner surface of the tank is of, or linedwith, electrically insulating material, the fact that the inner surfaceof the insulating material is liable to be damaged in this way mayeffect an increase in the frequency with which such insulating tanklinings have to be maintained.

It is an object of the present invention to provide an improved methodof electrolytically refining copper by the series process in which theconsumption of power for a given output of refined copper issubstantially less than that in series processes hitherto employed.

It is a further object of the invention to provide a method of andapparatus for electrolytically refining copper by the series process inwhich the consumption of power for a given output of refined copper issubstantially less than that in series processes hitherto employed, inwhich the electrical efficiency can be arranged to approach the optimum,and in which the risk of side edges of electrodes damaging the innersurface of a tank when the electrodes are lowered into or raised fromthe tank is substantially reduced.

In accordance with the invention the method comprises forrning a copperstrip of indefinite length by a continuous casting process, cutting thisstrip into lengths such that plates having the required superficial areaare formed, immersing the cut lengths as unrefined electrodes in seriesin an electrolyte solution contained in a tank whose inner surface is ofan electrically insulating synthetic polymeric material that issubstantially inert to the electrolyte solution, maintaining theelectrolyte solution at a temperature of at least 54C 129F), and passinga direct current through the electrolyte to cause impure copper from oneof the electrodes to be dissolved in the solution and deposited as purecopper on another of the electrodes.

The high softening temperatures of synthetic polymeric insulatingmaterials as compared with those of the insulating materials hithertoused for forming the inner surfaces of tanks used in the series processpermit the electrolyte solution to be maintained at a temperaturesubstantially higher than the temperature generally employed in anotherwise equivalent process with the result that the consumption ofpower is substantially reduced, thereby reducing the cost of a givenoutput of copper.

Preferably the tank has an inner lining of insulating polymeric materialsecured to the wall of the tank and this lining is preferably made ofpolyvinyl chloride. Where the lining is of polyvinyl chloride thethickness of the lining is at least 3.2 mm 4; in.) and the electrolytesolution is preferably maintained at a temperature of at least 63C(145F). Other synthetic materials of which the inner surface of the tankmay be formed include polythene, polypropylene, a co-polymer ofacrylonitrile, butadiene and styrene, a modification of this co-polymer,and other synthetic polymeric materials containing at least the chemicalelements of carbon and hydrogen.

Another advantage of using tank linings of synthetic polymericinsulating material lies in the fact that such linings requiresubstantially less maintenance than linings of mastic compositionshitherto used and, therefore, provide a further reduction in the overallcost of manufacture of electrolytically refined copper.

The unrefined electrodes may be supported in the electrolyte solution byany convenient means, for example by suspending the electrodes from abar by means of riveted straps or hooks passing through holes or intonotches formed in the upper part of the electrode so that a majorportion of each electrode is immersed in the electrolyte solution or sothat each electrode is totally immersed in the electrolyte solution.

Preferably, baffles of an electrically insulating material that issubstantially inert to the electrolyte solution are so positioned in thetank that flow of current that would otherwise occur around at leastsome of the immersed edges of electrodes is substantially reduced.

The baffles that substantially reduce current flow around immersed sideedges of electrodes preferably comprise sheets of a rigid, semi-rigid orresilient electrically insulating material, one such sheet or sidebaffle being positioned with its major surfaces vertical orapproximately vertical in the gap between side edges of the electrodesand each neighbouring side wall of the tank throughout substantially thewhole length of the groupof electrodes.

In the event that side edges of a group of electrodes being introducedinto the tank are not in substantial alignment with the tank, theprojecting side edges will be prevented from scoring or otherwisedamaging the inner surface of the tank by the intervening side baffle ofinsulating material which is expendable and can be replaced if it isdamaged by side edges of electrodes to such an extent that it can nolonger serve the purpose for which it was intended. The thickness ofeach side baffle in relation to the distance between the side edges ofthe electrodes and the neighbouring side wall of the tank will not be sogreat as to impede to an undesirable extent flow of the electrolytesolution.

The baffles that substantially reduce current flow around the immersedbottom edges of electrodes also preferably comprise sheets of a rigid,semi-rigid or resilient electrically insulating material but, in thiscase, the bottom baffles are positioned with their major surfacesvertical or approximately vertical in the gap between the base of thetank and the bottom edges of the electrodes in such a way that eachbottom baffle extends transversely of those walls of the tank which areadjacent the side edges of the electrodes throughout at leastsubstantially the whole of the width of the electrodes and the bottombaffles are mutually spaced along the length of the tank.

Slime released from the impure copper is permitted to sink between thebottom baffles and to settle on the base of the tank. Preferably theupper edges of the bottom baffles are approximately level with or areslightly below the bottom edges of the electrodes and each of theseupper edges is preferably chamfered or otherwise so shaped as to reducethe tendency for slime to settle upon it. Preferably, also, the bottombafi'les extend parallel or approximately parallel to the electrodes andin this case the spacing between the adjacent bottom baffles ispreferably less than that between adjacent electrodes so that there isalways at least one bottom baffle positioned below and between eachadjacent pair of electrodes.

Since the side baffles serve to reduce substantially the tendency fordirect current to flow around immersed side edges of electrodes and thebottom baffles serve to reduce substantially the tendency for directcurrent to flow around the immersed bottom edges of electrodes, theelectrical efiiciency of the series refining process is substantiallyincreased.

Each sheet of rigid, semi-rigid or resilient insulating materialconstituting a baffle is preferably of solid form, but the use of aperforated sheet or of a sheet of open-work or mesh-like form is notexcluded from the invention. Preferably the baffles comprise aninsulating synthetic polymeric material, for instance a polyvinylchloride composition; other polymeric materials of which the baffles maybe formed include polythene, polypropylene, co-polymers ofacrylonitrile, butadiene and styrene, modifications of these co-polymersand synthetic polymeric materials containing at least the chemicalelements of carbon and hydrogen.

The bottom baffles are preferably integral with, or inter-connected to,each other and form a self-supporting lattice-work structure. Preferablythe lattice-work structure comprises transversely extending bottombaffles interconnected by, or integral with, a pair of longitudinallyextending elongate members of a rigid, semirigid or resilientelectrically insulating material, each of which extends along the lengthof the tank adjacent a side wall of the tank and is supported on thebase of the tank. Each of these elongate members is preferably in theform of a strip which is arranged with its major surfaces vertical orapproximately vertical. The bottom edges of the bottom baffles andlongitudinally extending strips may be spaced from the base of the tankover the whole or part of their lengths to permit slime to settle morereadily on the base of the tank. Alternatively, the bottom edges of thebottom baffles and longitudinally extending strips may be integral with,or connected to, a base wall of rigid, semi-rigid or resilientelectrically insulating material separable from the tank, therebyforming a removable inner container into whichslime settles. In theseries process bottom baffles integral with, or connected to, a basewall separable from the tank serve to reduce substantially the risk ofcopper-bottoming occurring, that is to say the for mation of alongitudinally continuous path of copper deposited on electricallyconductive slime which has settled along the base of the tank, becausethe bottom baffles interrupt the electrical continuity of the slimealong the tank. The upper edge of each longitudinally extending stripmay extend above the upper edges of the bottom baffles and may be soshaped as to provide support for the bottom edges of the electrodes.

Where the bottom edges of the bottom baffles are integral with, orconnected to, a base wall separable from the tank, this base wall may beof sufficient thickness to protect from mechanical damage the base wallof the tank in the event that an electrode supported above the bottombaffles should inadvertently drop between two adjacent bottom baffles.Alternatively, or additionally, one or each neighbouring major surfaceof each adjacentpair of bottom baffles may have projecting outwardlyfrom the surface for a part but not the whole of the distance betweenthese major surfaces, at least one fin arranged with its major surfacesvertical or approximately vertical, the or each projecting fin servingto support on its upper edge an electrode should the electrodeinadvertently drop between two adjacent bottom baffles, therebyproviding protection against mechanical damage for the base wall of thetank. An alternative self-supporting lattice-work structure which willalso provide protection for the base wall of the tank against mechanicaldamage should an electrode inadvertently drop from its supporting means,may be in a form similar to that of a honeycomb and comprise two sets oftransversely extending bottom baffles, the baffles of each set beinginclined at an angle to one another and to the electrodes. In all casesthe upper edges of the bottom baffles and, when present, thelongitudinally extending strips and/or projecting fins are preferablychamfered or otherwise so shaped as to reduce the tendency for slime tosettle on them.

The side baffles are each preferably suspended in the electrolytesolution by means of hooks or other means carried on the upper edge ofthe sheet constituting the side bafile and engaging the upper edges ofthe electrodes or the means supporting the electrodes and in this casethe side baffles will be suspended from the electrodes or their means ofsupport as the electrodes are introduced into the tank. When s0suspended the side baffles will be immediately adjacent the side edgesof the electrodes. Alternatively, the side baffles may be suspended fromthe rim of the tank wall.

In a further alternative construction, along the whole or at spacedpositions along its bottom edge, each side baffle may be integral withor connected to one of the longitudinally extending elongate members ofthe lattice-work structure incorporating the bottom baffles.

Preferably where electrolyte solution is passed through a port or portsin the side walls of the tank the height of the side baffles in relationto the depth of the electrolyte solution and the relative extent towhich the side baffles are immersed in the electrolyte solution are suchthat cross flow of electrolyte solution is encouraged to take place overthe upper edge of one side baffle, through the plurality of gaps betweenthe electrodes and under the lower edge, or through apertures formedalong or adjacent the lower edge, of the other side baffle, or viceversa.

The present invention also includes apparatus for use in theelectrolytic refining of copper as hereinbefore described.

The invention will be further illustrated by a description, by way ofexample, of preferred apparatus for use in a method of electrolyticallyrefining copper by the series process, wherein unrefined electrodes areimmersed in an electrolyte solution contained in a tank and maintainedat a temperature of at least 63C (F), with reference to the accompanyingdiagram matic drawings, in which:

FIG. 1 is a fragmental side view, partly in section and partly inelevation, of the tank of electrolyte solution in which a group ofelectrodes is immersed, a side wall of the tank being omitted;

FIG. 2 is a fragmental cross-sectional view of the tank taken on theline ll II in FIG. 1;

FIG. 3 is a fragmental sectional view taken on the line III III in FIG.2; and

FIG. 4 is a fragmental sectional view, similar to the view shown in FIG.3, of an alternative form of selfsupporting lattice-work structureincorporating bottom baffles.

Referring to FIGS. 1 to 3, a group of electrodes 2 is suspended in andmutually spaced along the length of a tank 1 containing electrolyte 3with the major surfaces of the electrodes extending transversely of thetank and arranged in substantially vertical planes and with their bottomedges spaced approximately 300 mm from the base of the tank. The tank 1is lined with a layer of polyvinyl chloride having a thickness of 3.3 mmand has a length of 4.4 meters, a width of 1.2 meters and a depth of 2.1meters; the electrodes have a width of 1.0 meter.

Solid sheets 4 of rigid polyvinyl chloride constituting side bafiles aresuspended from the support means (not shown) from which the electrodes 2are suspended and are positioned between the side edges of theelectrodes and the neighbouring side walls of the tank. Each side bafflehas a height of approximately 1.65 meters, a length of approximately 4.4meters and a thickness lying within the range 5 10 mm.

Positioned in the gap between the base of the tank 1 and the bottomedges of the electrodes 2 is a self-supporting lattice-work structure 5made of rigid polyvinyl chloride and incorporating bottom baffles 6arranged transversely of the tank 1 substantially parallel to theelectrodes 2 with their major surfaces lying in vertical planes. Themutual spacing between the bottom baffles 6 is such that a bottom baffleis positioned between each pair of adjacent electrodes 2. Integral withthe ends of the bottom baffles 6 are two longitudinally extending,vertically disposed strips 7 which rest on the base of the tank 1 tosupport the structure 5 and which have castellations 8 in the bottomedges to permit slime to settle more readily on the base of the tank.The height of the bottom baffles 6 is such that their upper edges arepositioned slightly below the bottom edges of the electrodes 2 and theirbottom edges are spaced from the base of the tank 1 to permit slime tosettle over substantially the whole of the base of the tank. Each bottombaffle 6 has integral with each of its major surfaces two outwardlyprojecting fins 9 which extend over approximately two-thirds of thedistance between adjacent bottom baffles. The projecting fins 9 serve tosupport an electrode 2 should it inadvertently drop between adjacentbottom baffles 6, thereby projecting the base of the tank frommechanical damage. The upper edges of the bottom baffles 6, the strips 7and the projecting fins 9 are chamfered to reduce the tendency for slimeto settle on them.

In the alternative form of self-supporting lattice-work structure shownin FIG. 4 two sets of bottom baffles l6 and 26 extend transversely ofthe tank and are inclined to one another and to electrodes (not shown)suspended above them. The bottom baffles 16 and 26 are integral with oneanother and with longitudinally extending strips 17 and are so arrangedthat they will support an electrode should it inadvertently drop fromits support means, thereby protecting the base of the tank frommechanical damage.

What we claim as our invention is:

l. A method of electrolytically refining copper by the series processwhich comprises forming a copper strip of indefinite length by acontinuous casting process, cutting this strip into lengths such thatplates having the required superficial area are formed, immersing thecut lengths as unrefined electrodes in series in an electrolyte solutioncontained in a tank whose inner surface is of an electrically insulatingsynthetic polymeric material that is substantially inert to theelectrolyte solution, maintaining the electrolyte solution at atemperature of at least 54C (129F), and passing a direct current throughthe electrolyte solution to cause copper from one of the electrodes tobe dissolved in the solution and deposited as pure copper on another ofthe electrodes, wherein baffles of an electrically insulating materialthat is substantially inert to the electrolyte solution are sopositioned in the tank that flow of current between major facingsurfaces of adjacent electrodes is not impeded and flow of current thatwould otherwise occur around at least some of the immersed edges ofelectrodes is substantially reduced.

2. A method as claimed in claim 1, wherein the baffies are separablefrom the tank.

3. A method of electrolytically refining copper by the series processwhich comprises forming a copper strip of indefinite length by acontinuous casting process, cutting this strip into lengths such thatplates having the required superficial area are formed, immersing thecut lengths as unrefined electrodes in series in an electrolyte solutioncontained in a tank whose inner surface is of an electrically insulatingsynthetic polymeric material that is substantially inert to theelectrolyte solution, maintaining the electrolyte solution at atemperature of at least 54C (129F), and passing a direct current throughthe electrolyte solution to cause copper from one of the electrodes tobe dissolved in the solution and deposited as pure copper on another ofthe electrodes, wherein current flow that would otherwise occur aroundat least some of the immersed edges of electrodes is substantiallyreduced by baffles comprising sheets of an electrically insulatingmaterial that is substantially inert to the electrolyte solution, a sidebaffle being positioned between side edges of the electrodes and eachneighbouring side wall of the tank throughout substantially the wholelength of the group of electrodes with its major surfaces substantiallyvertical and a plurality of bottom baffles being positioned with theirmajor surfaces substantially vertical in the gap between the base of thetank and the bottom edges of electrodes in such a way that each bottombaffle extends transversely of those walls of the tank which areadjacent the side edges of the electrodes throughout at leastsubstantially the whole of the width of the electrodes and the bottombaffles are mutually spaced along the length of the tank.

4. A method as claimed in claim 3, wherein the bottom baffles areintegral with, or connected to, each other and form a self-supportinglattice-work structure.

5. A method as claimed in claim 1, wherein the electrolyte solution ismaintained at a temperature of at least 63C (F).

1. A METHOD OF ELECTROLYTICALLY REFINING COPPER BY THE SERIES PROCESSWICH COMPRISES FORMING A COPPER STRIP OF INDEFINITE LENGTH BY ACONTINUOUS CASTING PROCESS, CUTTING THIS STRIP INTO LENGTHS SUCH THATPLATES HAVING THE REQUIRED SUPERFICIAL AREA ARE FORMED, IMMERSING THECUT LENGTHS AS UNREFINED ELECTRODES IN SERIES IN AN ELECTROLYTE SOLUTIONCONTAINED IN A TANK THOSE INNER SURFACE IS OF AN ELECTRICALLY INSULATINGSYNTHETIC POLYMERIC MATERIAL THAT IS SUBSTANTIALLY INERT TO THEELECTROLYTE SOLUTION, MAINTAINING THE ELECTROLYTE SOLUTION AT ATEMPERATURE OF AT LEAST 54*C (129*F), AND PASSING DIRECT CURRENT THROUGHTHE ELECTRODES TO BE DISSOLVED IN THE COPPER FROM ONE OF THE ELECTRODESTO BE DISSOLVED IN THE SOLUTION AND DEPOSITED AS PURE COPPER ON ANOTHEROF THE ELECTRODES, WHEREIN BAFFLES OF AN ELECTROLYTE SOLUTION MATERIALTHAT IS SUBSTANTIALLY INNERT TO THE ELCTROLYTE SOLUTION ARE SOPOSITIONED IN THE TANK THAT FLOW OF CURRENT BETWEEN MAJOR FACINGSURFACES OF ADJACENT ELECTRODES IS NOT IMPEDED AND FLOW OF CURRENT THATWOULD OTHERWISE OCCUR AROUND AT LEAST SOME OF THE IMMERSED EDGES OFELECTRODES IS SBSTANTIALLY REDUCED.
 1. A method of electrolyticallyrefining copper by the series process which comprises forming a copperstrip of indefinite length by a continuous casting process, cutting thisstrip into lengths such that plates having the required superficial areaare formed, immersing the cut lengths as unrefined electrodes in seriesin an electrolyte solution contained in a tank whose inner surface is ofan electrically insulating synthetic polymeric material that issubstantially inert to the electrolyte solution, maintaining theelectrolyte solution at a temperature of at least 54*C (129*F), andpassing a direct current through the electrolyte solution to causecopper from one of the electrodes to be dissolved in the solution anddeposited as pure copper on another of the electrodes, wherein bafflesof an electrically insulating material that is substantially inert tothe electrolyte solution are so positioned in the tank that flow ofcurrent between major facing surfaces of adjacent electrodes is notimpeded and flow of current that would otherwise occur around at leastsome of the immersed edges of electrodes is substantially reduced.
 3. Amethod of electrolytically refining copper by the series process whichcomprises forming a copper strip of indefinite length by a continuouscasting process, cutting this strip into lengths such that plates havingthe required superficial area are formed, immersing the cut lengths asunrefined electrodes in series in an electrolyte solution contained in atank whose inner surface is of an electrically insulating syntheticpolymeric material that is substantially inert to the electrolytesolution, maintaining the electrolyte solution at a temperature of atleast 54*C (129*F), and passing a direct current through the electrolytesolution to cause copper from one of the electrodes to be dissolved inthe solution and deposited as pure copper on another of the electrodes,wherein current flow that would otherwise occur around at least some ofthe immersed edges of electrodes is substantially reduced by bafflescomprising sheets of an electrically insulating material that issubstantially inert to the electrolyte solution, a side baffle beingpositioned between side edges of the electrodes and each neighbouringside wall of the tank throughout substantially the whole length of thegroup of electrodes with its major surfaces substantially vertical and aplurality of bottom baffles being positioned with their major surfacessubstantially vertical in the gap between the base of the tank and thebottom edges of electrodes in such a way that each bottom baffle extendstransversely of those walls of the tank which are adjacent the sideedges of the electrodes throughout at least substantially the whole ofthe width of the electrodes and the bottom baffles are mutually spacedalong the length of the tank.
 4. A method as claimed in claim 3, whereinthe bottom baffles are integral with, or connected to, each other andform a self-supporting lattice-work structure.
 5. A method as claimed inclaim 1, wherein the electrolyte solution is maintained at a temperatureof at least 63*C (145*F).